Plug-in amp/watt power meter

ABSTRACT

A power meter has a measuring circuit composed entirely of analog components that measures the instantaneous current draw of one or more electrical devices, such as home appliances. The power meter may be in the form of a hand-held device that includes elongated connections that allow a homeowner to measure the current draw of an electrical device without significant displacement of the electrical device. In addition to measuring current draw, the power meter may provide an estimated wattage consumed by the measured electrical devices.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application of U.S. Ser. No.11/844,813, filed Aug. 24, 2007, which claims the benefit of U.S. Ser.No. 60/823,588, filed Aug. 25, 2006, the disclosure of whichincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to power meters and, more particularly, toa power meter to which the collective current draw of multiple loads ismeasured using a measuring circuit composed entirely of analogcomponents.

Whether it be as a matter of general interest or to determine the sizeneeded for an auxiliary power supply, such as an electric generator,homeowners are increasingly interested in the energy use associated withthe electric load of the home and, more particularly, of selectedelectrical loads. The total electrical load of a home may be determinedthrough monitoring the utility power meter typically located exteriorlyof the home. However, determining the electrical load, i.e., currentdraw, of selected electrical loads is more difficult.

One approach is to electrically isolate all loads except those to betested and then visually inspect the utility power meter. A drawback ofsuch an approach is that all loads not to be measured, of which theremay be dozens for a single home, must be electrically isolated.Alternately, the circuit breakers for the circuit branches loaded by theelectrical devices not to be measured may be thrown OFF. In the case ofthe latter, the homeowner would still be required to electricallyisolate loads of a given circuit branch if other electrical devices thatload the given circuit are to be measured. Regardless of which approachis taken, it can be time-consuming to electrically isolate theappropriate electrical devices. Moreover, if the homeowner wanted tomeasure the energy usage over time, the electrical isolation would berequired throughout the measurement interval, which may be undesirableand impractical.

As such, a number of in-line power meters have been designed that allowcurrent to be supplied to an electrical device through the power meteritself when interconnected between a wall outlet and the electricaldevice. These devices typically include rather complex digital circuitsthat measure various electrical parameters associated with the energyusage of an electrical device, such as an appliance. These parametersinclude instantaneous values, such as instantaneous current, as well astime-based values, such as average current. Moreover, some power metersmay be programmed to include cost information associated with energyusage so that a homeowner can monitor the cost of the energy usage of agiven electrical device.

These conventional power meters, which can be quite costly to theconsumer because of the complexity of the measuring circuitry and thefunctionality provided, are designed to be wall-connected devices. Thatis, the power meter will include a back-mounted electrical plug thatplugs into a conventional wall outlet. The power meter will also includea single front mounted outlet into which the electrical plug of anelectrical device to be measured can be plugged. Outside their cost,these conventional power meters are generally practical if the outlet towhich the power meter is connected is accessible and viewable.

For example, most homeowners connect the power cord of a refrigerator toa wall outlet that is positioned behind the refrigerator. Thus, to makeuse of a conventional power meter, the homeowner would be required towheel the refrigerator away from the wall a sufficient distance for thehomeowner to connect the power meter. To be able to read the powermeter, the homeowner would also be required to wheel the refrigeratorout a sufficient distance so that the display panel of the power metercould be viewed. For a typical refrigerator, this may require that thehomeowner wheel the refrigerator several feet away from the wall outlet.To measure the energy usage over time and be able to visually read thedisplay panel, the homeowner would be need to keep the refrigeratorwheeled away from the wall outlet or wheel the refrigerator away eachtime the homeowner desired to read the power meter.

Another drawback of conventional power meters is that a single outlet isprovided for connecting a single electrical device to the power meter.To measure the electrical usage of multiple electrical devices requiresthe homeowner to connect each of the electrical devices to amulti-outlet receptacle and then connect multiple electrical devices tothe multi-outlet receptacle. The power meter may measure the collectiveenergy usage, but the power meter would have to be positioned insufficient proximity to all of the electrical devices to be measured.Alternately, multiple extension cords could be used to link theelectrical devices to the wall-mounted power meter with the additionalcost and disruption associated with multiple extension cords strewnabout the home.

BRIEF DESCRIPTION OF THE INVENTION

The present invention is directed to a power meter having a measuringcircuit composed entirely of analog components that measures theinstantaneous current draw of one or more electrical devices, such ashome appliances. The power meter may be in the form of a hand-helddevice, which includes elongated connections that allow a homeowner tomeasure and monitor a value of the current draw of an electrical devicewithout significant displacement of the electrical device. In additionto measuring current draw, the power meter may measure an estimatedwattage consumed by the measured electrical devices. Since the measuringcircuit lacks any digital circuitry, such as microprocessors, the powermeter may be light, small, and highly portable while providing a costsavings relative to predecessor digital-based power meters.

In one aspect of the invention, a power meter includes a plug insertableinto a conventional outlet and a receptacle adapted to receive one ormore plugs extending from various electrical appliances or other loads.Between the plug and the receptacles, the power meter includes an analogmeasuring circuit that can modify the electrical signal passing throughthe measuring device to determine the amperage drawn or watts consumedby the electrical device(s) connected to the power meter. This measuredor determined value for the particular electrical parameter is thendisplayed by the power meter in a manner that can be readily viewed by ahomeowner or other user.

In accordance with a further aspect, the invention contemplates a powermeter that includes a housing and a current measuring circuit disposedin the housing. The power meter further includes a first cord extendingfrom the housing and electrically connected to the measuring circuit.The first cord has a plug adapted to engage a conventional electricaloutlet. The power meter further includes a receptacle formed in thehousing and electrically connected to the current measuring circuit,wherein the receptacle is adapted to receive a conventional three-prongplug of an electrical device.

According to another aspect of the invention, the present inventioncontemplates a power meter that includes a plug adapted to be engagedwith a conventional electrical outlet and an outlet adapted to receive aplug of an electrical device. A measuring circuit composed entirely ofanalog components and electrically interconnected between the plug andthe outlet is adapted to measure an instantaneous current draw of theelectrical device.

Numerous other aspects, features, and advantages of the presentinvention will be made apparent from the following detailed descriptiontogether with the drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the best mode currently contemplated ofpracticing the present invention.

In the drawings:

FIG. 1 is a rear perspective view of a plug-in power meter constructedaccording to one embodiment the present invention;

FIG. 2 is a front perspective view of the power meter of FIG. 1;

FIG. 3 is a side perspective view of the power meter of FIG. 1;

FIG. 4 is a circuit diagram of the power meter of FIG. 1;

FIG. 5 is an elevation view of another embodiment of a power meteraccording to the present invention; and

FIG. 6 is an end view of a portion of the power meter shown in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

With regard now to the drawing figures in which like reference numeralsdesignate like parts throughout the disclosure, a plug-in power meterconstructed according to a first embodiment of the present invention isindicated generally at 10 in FIG. 1. The power meter 10 includes a plug12 disposed at one end that may be engaged with a conventionalelectrical outlet (not shown), and a cord 14 extending outwardly fromthe plug 12. The cord 14 contains conductive wires (not shown) thatenable electrical power to be supplied from the outlet to which the plug12 is connected, through the cord 14 to a receptacle 16 attached to thecord 14 opposite the plug 12. The receptacle 16 includes a number ofopenings 18 in a configuration similar to that of a conventional outlet,such that a plug (not shown) connected to a suitable electric device orappliance (not shown), such as a furnace, air conditioner, sump pump,microwave oven, refrigerator, freezer, toaster, coffee maker, computer,radio, and the like, can be inserted into the openings 18 in order toconnect the device or appliance to the outlet using the power meter 10,such that the device or appliance can be operated on power suppliedthrough the power meter 10.

The receptacle 16 also includes a housing 20 in which the openings 18are formed. The housing 20 can include an extension 21 projectingoutwardly from the housing 20 and in which the openings 18 are disposed.The openings 18 are electrically connected to a measuring circuit 24(best shown in FIG. 4) such that, when power is supplied to the deviceor appliance through engagement of the plug within the openings 18, theelectrical power passes through the measuring circuit 24 for measurementof the desired electrical parameter.

As best shown in FIG. 2, the housing 20 also includes a display 22generally opposite the openings 18. The display 22 is also operablyconnected to the measuring circuit 24 such that the value for anelectrical parameter as measured or determined by the circuit 24 can berepresented on the display 22. As best shown in FIG. 3, a switch 26 islocated on the housing 20, preferably on one side of the housing 20between the openings 18 and the display 22. The switch 26 is alsooperably connected to the measuring circuit 24 and selectively changesthe mode of operation of the circuit 24, such that the circuit 24 canmeasure and display one of two electrical parameters that can bedetermined by the measuring circuit 24. For example, in one embodiment,the switch 26 toggles the power meter between measuring current(amperage) draw and power (wattage) consumption of the connectedelectrical devices.

Referring now to FIG. 4, an exemplary circuit configuration 24 for thepower meter 10 includes an amperage measuring circuit 28 that isconnected to the power source or outlet via the plug 12, and to theelectrical device that is to be tested via the openings 18. The amperagedrawn by the appliance when operated is measured in an analog fashion byan amplifier 30 and resistors 32-38. The measured or determined valuefor the amperage is then directed to an analog-to-digital converter 40that functions only as a driver for the display 22. That is, theconverter 40 does not form part of the amperage/wattage measuringcircuit 28. The signal received by the converter 40 is converted into aformat that can readily be represented on the display 22 to illustratethe amperage or wattage value of the device or appliance plugged intothe power meter 10. When the switch 26 is in the proper position toindicate that the value for the amperage drawn by the appliance is to berepresented, this value is illustrated in a readable manner on thedisplay 22.

Alternatively, when the switch 26 is moved to the position indicatingthat the value for the watts consumed by the electrical device is to berepresented on the display 22, the measuring circuit 24 arrives at thisvalue by altering, or multiplying the measured or determined amperagevalue by a factor of 120 to provide an estimated value for the wattsbeing drawn by the device or appliance being tested. More particularly,when switch 26 is moved to the “WATT” position, the output of theamplifier 30 is presented across a feedback loop comprised generally ofresistors 34, 36. This causes the gain of the amplifier 30 to be changedfrom a unity gain to a gain factor of 120. In other words, the measuredcurrent draw is multiplied by the amplifier by 120 to provide anestimated power consumption for the connected electrical devices. Oneskilled in the art will appreciate that the gain factor of the amplifiermay be varied by selecting a resistor 36 with different impedance.Preferably, the value of resistors 32, 34 should be equal so that theamplifier 30 has a unity gain when switch 26 is the “AMP” position.

One skilled in the art will appreciate that the exemplary circuit shownin FIG. 4 includes additional electronic components that provide linebuffering and conditioning not specifically described herein.Additionally, one skilled in the art will appreciate that other circuitconfigurations using electronic components other than those shown in thecircuit are possible and considered within the scope of the presentinvention.

In a second embodiment on the present invention as shown in FIGS. 5-6,in which like components are designated with primed referencecharacters, the power meter 10′ includes the plug 12′, the cord 14′, andthe housing 20′ with the display 22′ and the switch 26′ as in theprevious embodiment. The cord 14′ is preferably formed to have a lengthsimilar to that for a normal extension cord. However, the power meter10′ also includes a second cord 42′ that extends away from the housing20′ opposite the cord 12′ to a receptacle 16′. It is understood thateither of the cords 14′ or 42′ may have any desired length. Thereceptacle 16′ includes multiple sets of openings 18′ in theconfiguration of a conventional electrical outlet, such that multipleplugs from multiple electric devices or appliances can be simultaneouslyconnected to the receptacle 16′ for determining a combined amperage orwattage for all of the appliances when in operation. Additionally, thereceptacle 16′ can include a selector device (not shown) that enablesthe power meter 10′ to determine the amperage or watt value for anycombination of the appliances connected to the receptacle 16′.

Various additional embodiments of the present invention are contemplatedas being within the scope of the following claims particularly pointingout and distinctly claiming the subject matter regarded as theinvention.

1. A display device for providing a visual output of at least oneparameter associated with the supply of electrical power to anelectrically operated device, comprising: a housing having a frontportion and a rear portion, wherein the housing includes a display areafor displaying information relating to the at least one parameterassociated with the supply of electrical power to the electricallyoperated device; circuitry disposed within the housing for providing anoutput to the display relating to the at least one parameter associatedwith the supply of electrical power to the electrically operated device;an elongated cord having a first end connected to the housing andinterfacing with the circuitry and a second end having an electricalconnector adapted to be connected to a source of electrical power; andan electrical connection area associated with the rear portion of thehousing and interfacing with the circuitry, wherein the electricalconnection area is adapted to engage a mating connector of a power cordinterconnected with the electrical device; and wherein power foroperation of the electrical device that is available at the source ofelectrical power is provided to the electrical device via the elongatedcord of the display device and transferred to the power cordinterconnected with the electrical device through the circuitry.
 2. Thedisplay device of claim 1 wherein the circuitry is configured todetermine an instantaneous power consumption of the electrical device.3. The display device of claim 2 wherein the display area is adapted todisplay a value indicative of the instantaneous power consumption of theelectrical device.
 4. The display device of claim 1 wherein thecircuitry is configured to determine an instantaneous current draw ofthe electrical device.
 5. The display device of claim 4 wherein thedisplay area is adapted to display a value indicative of theinstantaneous current draw of the electrical device.
 6. The displaydevice of claim 1 wherein the circuitry is configured to determine aninstantaneous voltage at the source of electrical power.
 7. The displaydevice of claim 6 wherein the display area is adapted to display a valueindicative of the instantaneous voltage at the source of electricalpower.
 8. The display device of claim 1 wherein the housing andelongated cord are configured to allow line of sight access to thedisplay area at a location remote from the source of electrical power.9. A display device for providing a visual output of at least oneparameter associated with the supply of electrical power to anelectrically operated device, comprising: a housing; an electricalparameter measuring circuit disposed in the housing; a cord extendingfrom the housing and electrically connected to the measuring circuit,and having a connector adapted to engage a source of electrical power;and a connection area integrally formed in the housing and electricallyconnected to the electrical parameter measuring circuit, wherein theconnection area is adapted to receive an electrical connector of anelectrical device.
 10. The display device of claim 9 further comprisinga display area on the housing generally opposite the connection area,wherein the display area is adapted to display one or more valuesassociated with the of the supply of electrical power to the electricaldevice.
 11. The display device of claim 10 wherein the one or morevalues include one or more of a wattage value, a current value, or avoltage value.
 12. The display device of claim 10 wherein the displayarea comprises a screen.
 13. The display device of claim 10 wherein theconnection area is configured to receive a pronged plug associated witha power cord of the electrical device.
 14. The display device of claim10 wherein the cord has a pronged plug adapted to be inserted into aconventional electrical socket.
 15. A display device for providing avisual output of at least one parameter associated with the supply ofelectrical power to an electrically operated device, comprising: ahousing; an elongated cord extending from the housing and including aplug adapted to be engaged with a conventional electrical outlet; anelectrical receptacle on the housing, wherein the electrical receptacleis adapted to receive a plug of the electrically operated device; ameasuring circuit contained within the housing and electricallyinterconnected between the cord and the electrical receptacle andadapted to measure a parameter associated with the supply of electricalpower to the electrical device; and a screen on the housing, wherein thescreen is adapted to display one or more values indicative of one ormore of the parameters associated with the supply of electrical power tothe electrical device.
 16. The display device of claim 15 wherein theone or more values includes a waif age value, a current value, or avoltage value.